Waste collection systems operating at sub-atmospheric or vacuum pressure for transport of waste by means of suction of air have been in use for many years and are well known to present an efficient, clean and convenient solution to the waste disposal problem. Such systems for suction transport of waste, hereinafter simply referred to as vacuum waste collection systems, have worked remarkably well in smaller and medium-sized residential and office building areas. However, as vacuum waste collection systems have been placed into service in larger and more dense residential and office building areas and/or areas with multi-story buildings of the high-rise type, the demands on the systems have increased considerably.
Attempts have been made to reduce the emptying and collection times by increasing the vacuum in the transport pipes of the system, but unfortunately such an increase of the vacuum will increase the danger of compacting the waste too much, resulting in a plug flow that may cause blockage in the pipes of the system. Such blockage may even shut down an entire branch line or transport line. Another problem related to the employment of increased vacuum levels is the noise that is generated by the resulting airflow through the waste chute in connection with the emptying. In addition, high levels of vacuum may force opened access ports to close rapidly and jam or even injure a person that is about to discharge a bag of waste.
Traditionally, a so-called predefined structured emptying order is used by the system by which waste chutes and transport pipes are emptied in a given order, normally starting with chutes close to the central waste collection point and working towards more remote chutes to avoid blockage in the main pipes.
It is also known to use so-called level-controlled emptying to optimize the performance of vacuum waste collection systems. In level-controlled vacuum waste collection systems, each waste chute is provided with a discrete level sensor for indicating the existence of waste being piled up to a predetermined level in the waste chute. When the waste reaches the predetermined level, the level sensor sends a level-indication signal to the control system. At level-controlled emptying, the control system gives higher priority to waste chutes with level indications, and empties such waste chutes on a “first-come first-serve” basis. In this way, the control system may change the predefined structured emptying order normally used by the system and direct the collection of waste to waste chutes with level indications.
Conventional level-controlled emptying has turned out to be effective at certain load conditions in smaller systems, leading to improved system performance. In larger and more complex systems however, level-controlled emptying tends to have an opposite effect, leading to frequent jumps between different branches of the system and thus inefficient use of the available waste collection resources.
Conventional level-controlled emptying is also inflexible in that once the level sensors have been arranged in the waste chutes, it is difficult to flexibly adapt the predefined levels so as to change the time margins of the vacuum waste collection system and optimize the operation of the system. The predefined level used in conventional level-controlled emptying may be too high to prevent overloading of waste chutes at high load in the system, whereas at low load in the system, the predefined level may be too low for optimal utilization of the resources. Another disadvantage is that the “first-come first-serve” principle does not consider the consequences of the order in which the waste chutes are emptied. For example, there is always the risk of overloading of a waste chute in a critical area, which is not first in the emptying queue.
One way of improving the utilization of the available resources in a vacuum waste collection system and avoiding many of the disadvantages of conventional level-controlled emptying is disclosed in our international application WO 01/05683. The idea here is to partition discharge valves, and hence corresponding waste chutes, into groups and perform controlled emptying of waste by opening discharge valves and initiating collection of discharged waste on a group basis. More particularly, the control system selects one group at a time for opening of discharge valves within the selected group. This approach has turned out to be particularly efficient for larger systems, especially in combination with level-controlled emptying. By performing level-controlled emptying on group level instead of performing level-controlled emptying for individual discharge valves many of the disadvantages of conventional level control are avoided, while the advantages thereof are still obtained.
Further improvements in recent years involve the use of adaptive prediction techniques for improved control of a vacuum waste collection system.
As disclosed in our international application WO 01/05684, future values of one or more operational parameters are adaptively predicted based on a number of consecutive waste level measurements in the system and the operation of the system is controlled accordingly. By using adaptive prediction techniques instead of simple and static rules of thumb, the reliability and efficiency of the overall waste collection system can be substantially improved.
As disclosed in our international patent application WO 2004/094270, selection of a hop to a next branch in a vacuum waste collection system having a multi-branch transport pipe system can be automated by means of an efficient next-hop selection procedure. For each of a number of possible next-hop candidates, representations of future waste chute load levels in a plurality of branches within the system are predicted, and a system consequence value is determined based on these predicted load level representations. Once the system consequence values for the next-hop candidates have been determined, a hop to a next branch is selected among those candidates that have the most favorable system consequence values.
Although many advances have been made within the field of waste management and waste disposal, there is still a potential for further improvements within the general framework of efficient control and operation of vacuum waste collection systems.
In particular, there is a general need to provide more energy-efficient solutions for transport of waste to the central waste collection point, while ensuring reliable operation of the vacuum waste collection system.